Common Bean Diseases

This fungal disease looks like spidery veins growing in the plant’s foliage, but then turns it brown. This can be fatal to your beans, but it can be eliminated with it with lime/sulfur spray or Bordeaux mix. It’s best to buy varieties that are adapted to the climate in your area or are resistant to the disease, such as Tendergreen.

This fungus attacks the leaves and the stems of the plant. It appears in the form of small rust-like flakes on your plants. This can be deadly to your plants, but only if the infection is allowed to become severe. If your plant is attacked, spray or dust the infected stems lightly with sulfur, garlic or a recommended fungicide — preferably organic. Dispose of any heavily infected plants.

Powdery mildew
A common problem in wet or humid climates, this looks like a white powder growing on the plant. It can be easily controlled by applying a sprinkling of sulfur to the leaves. Application will vary by the type of sulfur you purchase, so read the label carefully. Baking soda or potassium bicarbonate can also provide good control and it’s much easier for people with sulfur allergies or sensitive skin to handle. Garlic sprays can kill it as well.

Bean mosaic
This viral disease can be recognized by the manner in which it discolors foliage and forms distorted, twisted growth. It is rather difficult to control and would be best to simply plant bean varieties that are known to be resistant to this viral disease.

Photo courtesy of timparkinson at

Important notes about pest and disease control products

Citrus sprays
Citrus sprays mixed according to manufacturers directions, are great at controlling various pests, like the Mexican been beetle. You need to be sure the oils you use are natural and not a synthetic solvent scented and sold as “orange oil.”

Soap Sprays
Don’t apply soap sprays too heavily or on hot days as it can burn the foliage.

This natural insecticide was recommended for years as a control for Mexican bean beetles, but we recommend against its use as it has now been linked to various neurological disorders.

This is a great organic control for many bean fungal diseases, such as rust that can really make a dent in your bean crop. However, be careful using sulfur as misuse can be bad for you and the plants. Do not apply during high temperatures as it may burn foliage. It’s also rather harsh on the skin, and many people are allergic to sulfur. Don’t go overboard with the application of sulfur, adding too much will shock the soil and prevent your plants from growing properly.

As a final note on sulfur, never add it to — or apply it after you have recently used — hydrated lime, never.

Hydrated lime is something most people probably won’t use in your garden, unless you have a very acidic soil or use an organic pesticide made with the hydrated lime. Mixing these two can form hydrogen sulfide — a very dangerous compound. You don’t want that to happen! If you have applied hydrated lime and need to apply sulfur, just water in the lime really well and wait a few days to prevent this dangerous gas from forming.

{ 2 comments… read them below or add one }

Bryce 01.21.11 at 7:19 pm

My Scarlet runner beans and runner beans set but the small beans do not reach maturity, just wither to dry shells.
The plants look healthy.
Is this a lack of water or?????

mem 12.19.11 at 12:55 am

maybe you need more fertiliser?

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